I had a conversation about this with a CX employee (who was trying to convince me to join MPC). I decided not to, as CX does such a good job in honouring Emerald status. But CX does treat Diamonds very well (much better than EXP, but as non-mileage benefits). Example: 2-class planes with F cabin are Diamond-only in the F section (with C service), the F suites are left empty even in C seating is completely full. Lounge access (more guests, arrival service, access when not flying oneworld). Greater hand/checked luggage allowance than Emerald. Little things like that (maybe quite valuable for some). I've decided not to join (most of the same benefits also accrue when flying F on CX); of the Oneworld airlines CX is by far the best in honouring Oneworld benefits. I've started to reorient my travel to be able to fly CX more often, so they have generated new business because of their policies and execution.